In the last decades, in many countries a large rise in both the number of chicken and poultry farms, and in the number of animals per farm, has been seen. This situation has a serious consequence: it has caused an increasing need for new and better vaccines and vaccination programs in these countries.
Nowadays, most animals are immunized against a number of diseases of viral, bacterial and parasitic origin. Examples of viral diseases in poultry are Newcastle Disease, Infectious Bronchitis, Turkey Rhinotracheitis, Herpesvirus of Turkeys, Fowlpox, Infectious Bursal Disease, etc. Examples of bacterial diseases are Coryza, Salmonella infections, Pasteurella multocida infections and E. coli infections.
A new bacterial respiratory disease has surprisingly been observed in chickens and turkeys. The disease was seen in chickens that had been vaccinated against the bacterium Haemophilus paragallinarum, the causative agent of a disease called Coryza. Coryza is, as far as known, the only respiratory disease in chickens caused by bacteria belonging to the families of Pasteurellaceae and Neisseriaceae.
The symptoms of this new disease differ from the specific symptoms of Coryza. Coryza is mainly an infection of the upper respiratory tract. Infected animals show a serous to mucoid nasal discharge, facial edema and conjunctivitis. They do not, however, show the clinical signs of diseases of the lower respiratory tract, such as airsacculitis or coughing, pneumonic lungs or pleuritis.
Given the fact that the newly discovered disease clearly shows the clinical signs of a lower respiratory tract infection as described below, H. paragallinarum could be ruled out as the causative agent.
The newly discovered disease is characterized by the following clinical signs in chickens:
The first indication of this new disease is mild snicking. Two or three days later a small number of broilers usually develop a mild nasal discharge and/or mild facial edema, which disappear after 2-4 days. Snicking continues until the birds are processed. Within 1-3 days from the beginning of respiratory symptoms, evidence of a reduction in feed intake can be detected. This is associated with some increased mortality mainly from broilers succumbing to pneumonic lungs and pleuritis, often with thickened thoracic airsacs. From these lesions, E. coli is the dominant isolate. Subsequent losses are mainly associated with extensive airsacculitis.
Examination of live broilers at the start of the syndrome usually reveals no specific pathology. From the sinuses of affected broilers a Pasteurella-like organism can occasionally be isolated. After a couple of days, 30-60% of the broilers suffer from extensive involvement of, especially, the abdominal and thoracic airsacs.
Especially noticeable is the severe thickening of the airsac membranes. These airsacs often contain a copious amount of a creamy white-yellowish exudate. A somewhat velvety appearance of the airsac is also common. A whitish-creamy foamy exudate is often evident on the mesentery as well. Histopathology reveals a prominent exudative inflammatory process with a fibrinous exudate on the surface and within the membrane, with edema as well. Accumulation of plasma cells and heterophils are noticeable with some multinuclear giant cells and granulomatous infiltrations. No specific microorganisms are visible in sections with Ziehl-Nielsen and PAS staining. In live birds no pericarditis, perihepatitis or splenitis is usually seen.
From affected airsacs Pasteurella/Neisseria-like organisms were isolated. These isolates did not seem to be classic species in the sense that they do not, in spite of their relatedness to Pasteurella and Neisseria, belong to these species and some variation in their biochemical abilities has been noticed.
In turkey flocks in several parts of the world, a comparable infection of the upper respiratory tract was found. At first appearance, a low mortality was found, although at this moment mortality in flocks suffering from the disease can be as high as 5%.
The first clinical signs are comparable to infection in chickens: sneezing and nasal discharge. In some animals clinical signs of acute infection were seen. Examination of sacrificed animals showed edema of the lungs, fibrinopurulent pneumonia and often serofibrinous pericarditis and serofibrinous infection of the airsacs.
Bacteria were isolated from infected airsacs and purified. After purification, isolates were grown on rich agar dishes in order to obtain large quantities of pure pathogen.
In order to check for the validity of the Koch postulates, a group of S(pecific) P(athogen) F(ree) animals was infected with a mixture of isolates. After infection, they all showed clinical signs that were indistinguishable from those seen in field infections.
From the airsacs of these infected animals, bacteria were isolated that were serologically indistinguishable from the challenge strains.
Four similar highly homologous strains were isolated from the airsacs of sick chickens. One very similar strain was isolated from the airsacs of turkeys.
The strains were identified as being Gram-negative, aerobic rods. The various isolates show minor differences in their respective fermentation patterns. All strains, however, clearly belong to the same serotype, i.e. serum raised against each of the five strains (cross-)reacted with each of the strains.
One of the chicken strains was deposited at the Centraalbureau voor Schimmelcultures (CBS), Oosterstraat 1, PO.box 273, 3740 AG Baarn, The Netherlands, under Accession No. 400.92.